Trauma of nerve tissue is frequently followed by loss of sensory function or motor function. An injured nerve of the peripheral nervous system (PNS) may spontaneously regenerate and there may be recovery of function. However, recovery of function is rare following injury of the central nervous system (CNS).
Currently, nerve injury is treated by various suturing techniques in which the cut ends are carefully brought together prior to suturing. Another approach makes use of grafts or implants, referred to as nerve prostheses, which are fabricated from various materials or are harvested from the body of the patient (autografts) and are used as devices for bridging the gap between cut ends of nerve tissue. The most successful nerve grafts are the autografts. Typically, a nerve injury which is serious enough to justify the use of grafting is treated by an autograft which is surgically removed from the sural nerve.
The autografting procedure, which gives the best results compared to other grafting procedures when treating injuries of the PNS, has the disadvantage that the patient has to be surgically invaded to produce a graft of dimensions appropriate for treating the injured nerve. In several instances the sural nerve or other nerves that are commonly used as sources of grafts do not have dimensions which are appropriate for the injury. Another serious problem with the use of autografts is that their success rate when used with injury in the CNS is very low. Typically, a person with serious CNS injury, (e.g., spinal cord injury), remains paralyzed in spite of autografting. A major problem encountered in grafts at GNS lesions is that scar tissue forms at the site of the injury and advancing nerve fibers (axons) are intercepted by scar. As a result, injured and cut nerve fibers do not reconnect and function is not restored.
Studies of reconstruction of damaged nerve tissue have been described by De Medinaceli et al., in Exp. Neurol., 81, 459 (1983); Exp. Neurol., 81, 469 (1983); and Exp. Neurol., 81, 488 (1983). These studies describe the physical and chemical factors which must be considered in order to achieve "reconnection". These studies described techniques in which substantial motor function was returned in rats following transaction and crushing of the sciatic nerve. In none of these studies, however, were severed sciatic nerve ends separated to a substantial degree prior to reconnection.
In Neuropath. Exp. Neurol., 41, 412 (1982); and Exp. Neurol., 76, 361 (1982), Lundborg et al. describe studies in rats in which a substantial gap was created between severed sciatic nerve ends, followed by attempts to achieve regeneration and recovery of function by unsheathing the cut ends in a silicone tube. Partial regeneration was found for 6 mm and 10 mm gaps, however, none was found for gaps of approximately 15 mm.
Thus, a need still exists for a method by which severed nervous system tissue can be regenerated across a substantial gap. Additionally, the regenerated nerve tissue should have the ability to restore motor function in the affected extremities.